We are using different muscle types of the chicken as model systems to investigate the mechanisms which regulate the biogenesis and degradation of specific well-defined eucaryotic proteins. Elucidation of these mechanisms is required for an in-depth understanding of both normal cell-function and the breakdown of normal cell function which is associated with certain disease states. We have recently made the significant observation that skeletal, cardiac and smooth (gizzard) muscles of the chicken synthesize secretory proteins. These observations are surprising since, unlike tissues such as liver and pancreas, muscle has not previously been considered to be a "secretory" tissue. We have identified the secretory protein synthesized by skeletal and cardiac muscles as apolipoprotein A1, the main protein component of the "high density" class of serum lipoprotein particles. We are in the process of identifying the 73,000 dalton secretory protein produced by gizzard muscle. The main goal of our research project is to investigate the regulation of synthesis of several intracellular enzymes (aldolase, glyceraldehyde-3-P dehydrogenase, and creatine kinase) and the regulation of synthesis and secretion of the muscle secretory proteins. These studies will involve measurements of specific mRNAs in these muscle types as determined in cDNA/mRNA hybridization experiments and measurements of relative rates of synthesis of the proteins in amino acid incorporation experiments conducted with intact muscle cells. Of major interest will be the work on the effect of development in vivo and of long term culture in vitro on the synthesis of these proteins by the muscle types. These latter experiments may help to identify the endogenous and exogeneous "signals" which ultimately regulate the synthesis of these intracellular and secretory muscle proteins.